More plastic, fewer oysters?

By Erica Cirino, Safina Center Launchpad Fellow

2016 started off with a dire prediction for the world’s oceans: By 2050, the seas will contain more plastic—by weight—than fish. There’s an estimated 8 -12 million metric tons of plastic making its way into the oceans each year. And as the plastic mess in the oceans grows, so do concerns over the health of the marine creatures living in it.

While it’s known that plastic bags and bottles pose a risk to sea creatures, a lesser-known threat is now coming to light, one that’s created when ocean waves and wind pulverize the plastic bags, bottles and other trash that ends up in the seas: “microplastics.”

These tiny plastic pieces are about the same size and shape as the algae eaten by some marine animals. How microplastics affect marine animals is not well understood.

Microplastic poses a growing concern in oceans and other aquatic habitats. Photo: 5Gyres, courtesy of Oregon State University

But in recent years scientists have found that crustaceans that consume microplastics have a hard time reproducing. Going off a hunch that microplastics may affect the fertility of other filter feeders, researchers at the French Institute for the Exploitation of the Sea started feeding oysters microplastics.

The researchers observed two groups of oysters: one fed a normal diet of algae and another fed a mix of algae and microplastics. The oysters fed the mixed diet swiftly sucked up the microplastics as easily as they did algae. After two months the researchers have found microplastics take a toll on both oyster digestion and reproduction.

Oysters that consume microplastics eat more algae and absorb it more efficiently, says Arnaud Huvet, marine physiologist at the French research center and lead author of the study. This is because oysters expend extra energy to pass plastic through their digestive systems, increasing the rate at which they digest algae.

While the digestion of microplastics diverts some energy away from reproduction, oysters’ ability to reproduce is almost halved: Female oysters produce fewer and smaller eggs while male oysters produce slower-swimming sperm. Offspring produce more slowly. The cause? Blame the chemicals that make up microplastics.

During digestion microplastics appear to leach hormone-disrupting chemicals into oysters’ bodies, says Huvet. These chemicals, also called “endocrine disruptors,” are known to lead to diminished fertility and an increased cancer rate in laboratory animals, wildlife and humans. They’re found in all kinds of everyday products, including cosmetics, pesticides and plastics.

Can the microplastics accumulating in oysters’ bodies harm the animals or humans that eat them? Right now, Huvet says, that’s unclear. But he points out his study adds to a slowly growing body of evidence highlighting the health impacts of plastic pollution in the oceans.

Seafood expert Elizabeth Brown-Hornstein agrees: “This study provides further evidence that plastic litter has far-reaching effects on the oceans and that there is an urgent need to take meaningful action to tackle this issue.”

Learn more about plastic and other marine pollution, and what you can do to help, here.